Ensuring the quality and appropriate state of sleep is essential for maintaining one's health. It is necessary to understand a sleep state, including an amount of sleep time from when a person goes to bed to when the person wakes, the depth of the sleep, and so on, in order to evaluate the sleep state. The devices disclosed in Patent Literature 1-3 have been proposed as devices for understanding such a sleep state.
Patent Literature 1 discloses a device that detects a measurement subject's body movement in a non-contact manner by using an infrared sensor provided in a position distanced from the measurement subject, and determines that a segment, in which a change amount in a signal outputted from the infrared sensor in a short interval of time exceeds a threshold with high frequency, is a segment in which the measurement subject is in a waking state.
Patent Literature 2 discloses a device that detects a measurement subject's body movement using an accelerometer attached to the measurement subject, calculates a fluctuation amount in a detection signal based on a time derivative of the output of the accelerometer, and determines that a segment, in which the fluctuation amount exceeds a threshold with high frequency, is a segment in which the measurement subject is in a waking state.
Patent Literature 3 discloses a device that determines a sleep state of a measurement subject using a vibration sensor that detects vibrations in a location where the measurement subject is sleeping.